Method for vacuum dehydration and apparatus therefor



July 15, 1969 METHOD FOR VACUUM DEHYDRATION AND APPARATUS THEREFOR Filed Aug. 29, 1967 A- VAN GELDER 4 Sheets-Sheet 1 PRODUCT IN (D PRODUCT f PREPARATION l r- I I T i i PRODUCT EVAPORATIVE PRODUCT WATER l VAPOR PRODUCT CONDENSER CELL-FILLER WATER? WATER WATER lwATER VACUUM PRODUCT INDUCTION PUMP DEHYDRATOR 42 GENERAToR WAT-ER WATER} wATERf WATER VAPOR PRODUCT CELL CONDENSER ELL- DISCHARGE CLEANER STEAM HOT WATER PRODUCT CONVEYOR A LWATER VACUUM PRODUCT LIQUID-NITROGEN PUMP PACKAGING TANK WATER INVENTOR. ARTHUR VAN GELDER ouT BY 4 i 27" fM FIG.

July 15, 1969 A. VAN GELDER METHOD FOR VACUUM DEHYDRATION AND APPARATUS THEREFOR Filed Aug. 29, 1967 4 Sheets-Sheet 2 INVENTOR. ARTHUR VAN GELDER ATTY July 15, 1969 v A. VAN GELDER 3,455,031

METHOD FOR VACUUM DEHYDRATION AND APPARATUS THEREFOR Filed Aug. 29, 196"! 4 Sheets-Sheet 5 T'- r' J a F2 0 7 n ---1 I NV ENTOR.

ATTY

July 15, 1969 A. VAN-GELDER 3,455,031

METHOD FOR VACUUM DEHYDRATION AND APPARATUS THEREFOR Filed Aug. 29, 1967 4 Sheets-Sheet 4 Willi.

INVENTOR.

ARTHUR VAN GELDER ATTY United States Patent 01 U.S. Cl. 34-5 21 Claims ABSTRACT OF THE DISCLOSURE This invention relates to vacuum dehydration of products, particularly food products, in separately controlled tubes in which dehydration is brought about by induction heating of the tube. Each tube is wrapped with an electrically conductive tubing suitably insulated, through which a liquid coolant may be circulated. In 50-60 cycle operation copper wire, suitably insulated, may be used in place of tubing. The material to be dehydrated may be either liquid or solid and if it is liquid it must be pretreated to a snow-like quick frozen state. If the material is solid it is reduced to patty size cakes and may be either fresh or frozen. The prepared material is placed in specially designed electrically conductive carriers for loading in the tubes leaving enough space for the instantaneous removal of water vapor. The loaded tubes are subjected to induction heating under vacuum conditions, the vacuum source continuously drawing off water vapor at a high rate. Each tube is separately controlled, although usually operated in a plurality of vertical banks of three. Any one bank may be isolated from the remainder without interference with or danger to the entire operation. This means that the individual banks may be separately charged, separately operated, separately emptied and separately cleaned or repaired. The same is true for each tube in each bank. The invention covers both the apparatus for carrying out the process and the sequence of steps of the process.

The work with the prior results as demonstrated in the van Gelder Patent No. 3,253,344 which issued May 31, 1966 and in the van Gelder Patent No. 3,316,652, issued May 2, 1967, have produced such unusual and promising results, that further work caused new and dilferent steps to be performed and new and different apparatus to be devised, eventually leading to the-discovery and development of this invention.

Some objections have been made with respect to the prior methods particularly those involving the mixing of relatively small coated metal pieces with the material being dehydrated. This criticism has come both from the standpoint of processing and from the standpoint of inadvertent remainder of foreign particles in the finished food. While the precautions taken and the manner of using the coated metal pieces have reduced the possibility of any foreign matter remaining in the food to a remote mathematical speculation, nevertheless, there is that one chance of error which is completely eliminated in the method and apparatus disclosed herein.

Furthermore, the reduction in the number of steps and the simplification of the process and apparatus for conducting it have been illusive, but prime objectives of the present invention.

A better appearing product both in dry form and in reconstituted form have been objectives as well as a better product having natural flavor, aroma and taste, both the dry and reconstituted forms where food is involved, have also been important objectives.

It has been an object to limit the down time, for charging and discharging the apparatus of the system as well ice as the time required for cleaning and servicing the equipment. This has been provided by breaking up the system into independent units, any one of which can be isolated from the operation without disrupting the continuous operation of the system as a whole. This gives great versatility to the process and the apparatus in that any number of products can be handled simultaneously in the individual tubes.

Another objective has been the provision of carriers for handling the products during dehydration which are not only effective in induction dehydration, but may be used in any dehydration system where heat is used.

Further objects are to provide a construction of maximum simplicity, economy and ease of assembly and disassembly, also such further objects, advantages and capabilities as will fully appear and as are inherently possessed by the device and invention described herein.

The invention further resides in the combination, construction and arrangement of parts illustrated in the accompanying drawings, and while there is shown therein a preferred embodiment thereof, it is to be understood that the same is illustrative of the invention and that the invention is capable of modification and change and comprehends other details of construction without departing from the spirit thereof or the scope of the appended claims.

Referring to the drawings:

FIGURE 1 is the flow diagram of the process;

FIGURE 2 is a schematic layout in plan view for the principal apparatus involved, in typical arrangement;

FIGURE 3 is an elevational view of a portion of the dehydrating apparatus taken on the line IIIIII of FIG- URE 2 with the illustration of some ancillary equipment.

FIGURE 4 is an elevational view of the apparatus taken on the line IV-IV of FIGURE 2;

FIGURE 5 is a fragmentary side sectional view of a tube with a carrier inserted and projecting therefrom to show the carrier itself;

FIGURE 6 is a transverse sectional view of a tube particularly useful for liquid products, with the carrier shown in end view positioned within the tube;

FIGURE 7 is a transverse section view of a tube with a carrier useful for solid and patty products, in position therein and shown in end view;

FIGURE 8 is a fragmentary view of a tube in elevation showing the electrical conductive wrapping on the outside;

FIGURE 9 is a schematic end -view of a carrier loading mechanism; and

FIGURE 10 is a schematic view of the carrier unloading mechanism.

Referring now more particularly to the drawings wherein like reference numerals are used throughout to indicate the same or similar parts and with particular reference to FIGURE 1, there is shown a flow sheet of the steps required for the treatment of products in acordance with this disclosure, but it is to be understood that there is ancillary equipment of conventional design, such as boilers, motors, generators and the like, which must be used to make the system operate. The circle figures within each of the boxes down the center row of FIG- URE 1, generally represent a step in the process and the boxes at either side represent factors which alter and change the material undergoing treatment or which make the step possible. So far as practical, the circled numbers are referred to in the apparatus drawings to indicate where these several steps occur. The product for dehydration may be either liquid or solid. If liquid then the product preparation is preferably carried out in accordance with the copending application Ser. No. 607,517 filed Jan. 5, 1967, where the liquid is reduced to a quick frozen snow-like form and porous in structure. Any excess not used immediately may be held in frozen condition in the standard or evaporative freezer Solid material is formed in patty sized cakes and used fresh or held in the product prefreezer The product undergoing dehydration is first packed in a special carrier at the carrier filler station and is in turn placed in the tubular dehydrators where the pressure is reduced by vacuum pump simultaneously as the induction generator is energized to heat the product by induction current. The continuous vacuum removes the water vapor from the product dehydrators and conveys this to the vapor condensors in which a refrigerant or brine is circulated in a conventional manner. At and prior to the removal of the finished dehydrated product, nitrogen or some other non-toxic inert gas is used to break the vacuum in the tube. The product is removed from the carrier and placed directly on a conveyor to packaging. Vacuum (2) or nitrogen may be used in the packaging if desired, in accordance with conventional practice.

APPARATUS A suitable plant layout for operation of the process herein disclosed is shown in FIGURES 2. and 3. There are a plurality of straight glass tubes having sealable flanged coupling ends 11' and 12. The glass tubes described herein are standard Pyrex glass units, although any other make may be used. Any suitable dielectric material such as plastic or ceramic may be substituted for the glass so long as it is strong enough to withstand a vacuum of 100 microns. The glass tubes 10 shown are six inches in diameter and sixty inches long. This has been found to be a useful size, although the size may be adapted to meet special conditions as desired. For sticky products or products with highly tenacious odors, the interiors of the tubes may be coated with Teflon or other resistant substances, or a full removable sleeve (not shown) may be used. The tubes 10 are removably sealed in airtight engagement by cover plates 55.

As shown in the drawings and particularly with reference to FIGURE 8, the tubes are wound with electrically conducting material such as copper or aluminum tubing 14 or wire. In the 10,000 cycle operation the tubes 10 are wound in pairs of tubing 14 and 14a. They are wound coaxially in parallel with 45 turns or a total of 90 turns per glass tube 10 in a single layer. By ooaxially winding a more even distribution of heat is obtained. However, it is to be understood that any kind of winding which will produce an even distribution of heat over the distance will be satisfactory. The coaxially wound tubes 14 and 14a are connected to a suitable source of water supply (not shown) so that coolant water or other coolant material can be circulated therethrough to maintain a controlled constant temperature relation and keep the electrical resistance of the copper substantially equal throughout the entire length. The tubing 14 and 14a is insulated so as to prevent the possibility of conduction between the turns.

'For 60 cycle operation there are 1500 turns of W inch insulated copper tubing coaxially wound in six layers. At 440 volts this would deliver 6,000 B.t.u.s of heat and at 250 volts some 1,000 B.t.u.s. The tubing is used for the purpose of circulating a coolant therethrough wherever it is necessary. However, it has been determined that 9 to 8 gauge solid copper wire suitably insulated may be wound in 4 layers of 434 turns each and will accomplish the same result so far as heating is concerned but effects an economy in that no coolant is required for the operation. In the 60 cycle operation at 440 volts the number of windings will deliver 6,000 B.t.u.s and approximately 1,000 B.t.u.s at 250 volts.

In the induction heating for this apparatus a minimum heat is required over a maximum distance to obtain the magnetic afield to generate the heat. Accordingly, a large number of turns over a substantial length to obtain a minimum amount of energy to the tube is used so as to provide just sufiicient energy to obtain the latent heat of vaporization commensurate with the dehydration rate for each product. If there is too much heat there will be a melt of the product. If too little heat the rate and time of dehydration are greatly extended.

In the 10,000 cycle the coils .14 and 14a are conventionally connected to suitable generators such as the induction generator 15 as a suitable source of electric power. The power from the generator goes through a matching impedence transformer 16 and leads to a switch 19 which is opened and closed by individual thermocouples 17 which are directly responsive to the product temperature within the tube 10 as will be described later. The switch 19 in response to the activity of the thermocouple 17 delivers current to the coil 14 which has in turn a resonance capacitor 18 to control the resonance of the coil. It should be pointed out that instead of the matching impedence transformer 16 that a matching impedence capacitor may be substituted. In the 10,000 cycle operation the temperature control at the switch setting will oscillate on and off to control the heat going through the coils and keep the temperature constant at the setting.

In the 60 cycle operation the system is connected to the power line. The voltage passing to the coils 14 is directly controlled by the thermocouple 17 and this in turn is controlled by settings of standard voltage control means such as high-low settings or motorized settings which will produce an even flow of voltage for the setting. The control of the heat in the 60 cycle operation is the control of the DC current passing through a toroid.

The glass tubes 10 are preferably arranged in vertical tiers which are shown to be three in FIGURE 3, although they may be any suitable number. Each of the tubes 10 of the tier are connected by flange 12 individually to a connector 22. In connector 22 there is a valve 23 which is operable to isolate the tier from the rest of the apparatus and establish by opening valve 25, a connection with a source (not shown) of nitrogen gas at atmospheric pressure. In the normal operation of the equipment the valve 23 is open with the connection to the nitrogen gas source 25 closed during dehydration. The connector 22 couples the tier of tubes to a common manifold 24 through the isolation valve 23 which is preferably a butterfly valve. By closing the butterfly valve 23 the single tier of tubes is isolated from the operation of the rest of the system. It will be observed that by the addition of suitable valving, each individual tube 10 may be coupled directly to the manifold 24 for individual operation. The manifold 24 is a large capacity tube which may be formed of several sections leading to a condenser system, one of the condensers 26 being shown in FIGURE 1. The established vacuum for the system is maintained in the manifold 24 which continuously pulls the water vapor from the tubes 10 to the condenser system represented by condenser 26. The condenser system is coupled through suitable isolation valves 27 to a source of vacuum indicated by the line 28. By this means a vacuum is drawn through the entire condenser and manifold systems and into the individual tubes during the operation so that there is a standard and constant vacuum of the same quality maintained during the entire operation, regardless of how many tiers or individual tubes are connected. The condensers 26 are operated in pairs so that one unit may be in operation while the other unit is being defrosted. The construction of the condensers 26 is conventional with the usual condensing plates. Brine, or other refrigerant, is drawn from the brine tank 27 through one of the heat exchangers 29 and circulated through the plates to freeze the water vapor from the manifold 24 on the plates. One of the condensers 26 is shut off from the system by means'of valve 30 during defrosting, but each is of suflicient capacity for handling the volume coming from the manifold 24. The water of defrosting is collected in the shell of the condenser 26 and delivered to the tank 31 or to storage in tank 32 for use in the remainder of the system in supplement to or in substitution of the main water supply 33.

The individual tubes are operated with two types of carriers, depending upon the kind of material being treated. The carrier 34 shown in FIGURES 5 and 6 is a series of vertical plates 35 which are circular in shape conforming to the inner diameter of the tube but spaced therefrom slightly with the top portion 36 cut off to form an open space 37 between the top of each plate 35 and the interior of the glass tube 10. The plates 35 are of electrically conductive metal preferably aluminum. They are arranged vertically by means of spacers 38 so as to provide a separation between them sufficient to hold the product undergoing treatment. The spacers 38 and the plates are held together by tie rods 40 and tightening means 41 at either end. The carrier 34 shown in FIGURE 6 is primarily intended for liquid and semi-liquid products which have been reduced by pre-treatment to a snow-like frozen form.

Referring now to FIGURE 7, the carriers 42 shown therein have substantially square plates 39 which have their four corners cut as at 43. Again, they are spaced vertically by the spacers 38 and held together with tie rods 40 and holding means 41. It will be noted that the air space 44 between the edges of the plates 39 and the interior of the tube 10 is smaller than that of 37, but it will also be observed that additively the four open spaces 44 are substantially the equal in volume of the open space 37. The thermocouples 17 are preferably connected to a plate 35 or 39 of the carriers so that the temperature readings are directly determined by the temperature of the product undergoing treatment.

THE METHOD The method will be described with reference to the production of coffee, it being understood that variations in the times and temperatures will be required in accordance with the product undergoing treatment. This process presupposes that the coffee concentrate is pretreated in the form of a quick frozen powder of a porous nature. It is maintained under refrigeration until ready for treatment so that it remains in its ice condition.

This frozen snow-like material is delivered on a flat plate 50 which is adjustable vertically to substantially the same height as the conveyor basket 51, and is substantially the same length as the carrier 34 and of greater width. The carrier 34 is placed on the Hat table 50 which preferably is refrigerated to maintain the ice form of the product, placed longitudinally on the table with the fiat top portion 36 downwards so that it will not roll or move. The carrier 34 is thereby in position between two longitudinally conformed curved blades 52 which are actuated by hydraulic rams 53 to force them laterally toward the curvature of the outer form of the carrier 34'. Each blade conforms to one half of the arc described by the curved plates 35. The snow-like coffee powder is pushed between the several curved plates 35 of the carrier 34 in an exact Weighed amount necessary to completely fill the carrier 34. The rams 53 are activated by conventional means so that the curved blades 52 are moved inwardly from each side of the carrier. When the carrier 34 is filled the blades 52 meet at the top and completely surround the curvature of the carrier blades, the filled and shaped carriers are then removed and placed with the flat side 36 upwardly upon a movable conveyor basket 51 which runs on track 54, in vertically stacked form, three stacks high to conform with the number of tubes 10 in the tier, and as many wide as may be conveniently handled, and moved along the track 54 to the entrance end of a tier of tubes 10.

The isolation valve 23 of the tier is closed so that the tubes 10 have no contact with the manifold 24- and are therefore shut off from the source of vacuum. Nitrogen gas is then introduced into the tubes 10 through valve 25 and this brings the three tubes in the tier to atmospheric pressure without introducing oxygen. As soon as atmospheric pressure is restored the nitrogen supply valve 25 is turned off. Then the end plates 55 secured to the flanges II of the tubes 10 are opened to expose the interior of the tubes and, if the tubes have been in operation, the fully treated carriers 34 are withdrawn from each of the tubes in the tier. These treated carriers, if any, are placed in a separate portion of the basket 51 to be thereafter emptied and the contents transferred for storage or packaging. The newly filled carrier 34 on the basket 51 are then pushed axially into the single tier of three tubes to fill the same. The end plates 55 are then replaced and closed over the ends 11 of the tubes to make them vacuum tight and the thermocouples 17 adjusted for the product and the switches 19 set. A vacuum breather valve 56 is then opened so as to re-establish a vacuum in the charged single tier of three tubes. This is done to avoid vacuum shock through the opening of the butterfly isolation valve 23, which is the next in sequence and restores the tier to full operation.

This whole sequential operation, of course, may be programmed for automatic operation although it can be done manually as well. The vacuum in the newly charged tubes 10 is immediately brought down to the level of the system which is 1,000 microns or less. As soon as the thermocouples 17 register a temperature of the product of 15 F. or less, then the induction heating is turned on. In the induction heating where 10,000 cycles is the form used, the control is on and off in timed sequence with the setting of the switch 19 which is connected with the thermocouple 17 on the individual coils. On coffee when the 10,000 cycle is used, the first temperature is set at 28 F. and run for two and one-half hours on an on and off cycle. The cycles of every fifteen minutes, the temperature is increased 10 F. up to eighty degrees in a full four hours. Then it is raised to F. for a remaining hour or hour and a half at which time the product is dry, Le, a moisture content of less than two percent.

In the 60 cycle operation the vacuum is drawn in the same manner, but uses a toroid voltage regulator which regulates the heating of each of the tubes and maintains them continuously at the setting. Every product has its own evaporation rate at any particular time in the drying cycle. The toroid, using the product as the control as before, will continuously furnish the proper amount of current for the required B.t.u., sufiicient to equal the evaporation rate and will adjust itself in accordance with the demands of the product itself at any particular time in the evaporation cycle. This feature cannot be accomplished in the 10,000 cycle operation which depends upon on and otf action to accomplish the same result. The toroids, of course, are connected to the thermocouples 17 in contact with the product on the interior of the tube at all times in the manner before described.

During the induction heating the product is raised to its vaporizing temperature and the water of vaporization is drawn off from the tube 10 through the space 37 between the fiat top 36 of the carrier and the tube. This space 37 at the top is a necessary condition so that the water vapor may be withdrawn from the tube without disturbing the operation going on in the product. The immediate and quick withdrawal of vapor from each of the tubes is necessary in order to maintain the frozen condition of the product. If the vapor remained in the tube then the temperature would change with the pressure and reduce the product to a non-frozen state. Thus, the vapor is rapidly withdrawn from each of the tubes 10 through the connector 22, through the open butterfly valve 23 and into the manifold 24. The vapor is taken through the manifold 24 into the condenser 26. The vapor condenser as well as the entire system is maintained under vacuum through vacuum line 28 and valve 27 so that the water vapor coming in to the condenser is frozen onto plates through which refrigerant is circulated at a temperature below that of the product in the tubes, usually to 50 'F.

An alternative of this, the water vapor is conducted by the manifold 24 directly to the barometric leg of a steam injector system where no refrigeration or vacuum is required.

The system presents great versatility. One of the chief features is the quick establishment of vacuum in the individual tubes. There is so little volume of air to be evacuated in an individual tube 10 that the high vacuum required is almost instantaneous. The blee-der line and valve 56 prevent vacuum shock to the product and greatly assist in the rapid establishment of vacuum conditions without injury to the product. Therefore, there is no time lag and no opportunity for the product to melt or change form, thus preserving the original characteristic of the food itself without damage and without change.

Another feature in the versatility of this is that by adjustment of the thermocouples and individual Valving, it is possible to have a different product in each tier of tubes or in a series of tubes and remain in full operation of the whole system at all times.

At the completion of the drying cycle which renders the product dry, that is, with a moisture content of less than two percent, the butterfly valve 23 is closed and the cycle repeated. The removal of the finished product can be accomplished in many ways, but the one shown here for illustrative purposes only, is that the carriers 34 are placed onto the basket carrier 51. The sudden exposure to atmospheric conditions does not in any way affect the product upon removal. Because of the porous nature of the finished product the interstices have been filled with the nitrogen gas and this, even under the exposure to normal atmospheric conditions in the basket 51, does not permit any change in the product prior to packaging.

The finished material can be removed from the carriers 34 in numerous ways, but for example, they may be suspended over a trough and vibrating members which pass between the plates 35 are vibrated mechanically or electrically so as to shake and remove the dried powder from the carrier itself. It has been found by experience that this is accomplished easily and cleanly and that very little of the product remains on either the plates or on the carrier itself. The material falls to the trough into a hopper and then is transported immediately for packaging or storage. No further treatment or refrigeration is required for the product and if the individual packages are sealed with or without nitrogen, it has been found that the keeping qualities of the product do not change over a long period of time.

The vacuum dehydration of solid products such as patties and fish filets formed into patties, it is helpful to use a different type of carrier 42, shown in FIGURE 7. The solid products are shaped substantially four inches in diameter and sold meat such as ham, lamb and beef, and cut into four inch circular pieces approximately /8 to /2 inch thick. This has larger area contact plates 39 but are squared off on all four corners 43 so as to leave openings 44 adjacent the inner surface of the tube on all four sides so that vapor withdrawal may come from any angle within the tube 10. It will be observed that while the space 44 at the top of plate 39 is smaller than 37 of the circular plates 35 shown in FIGURE 6, the total amount of open area for the removal of the vapor is approximately the same in both forms so that there is no hindrance to or change in the rapid removal of the water vapor.

The use of patties or filets does not require the quick freeze prior treatment, although they may be quick frozen for storage purposes. This is due to the rapid establishment of vacuum within the tube. The rapid establishment of vacuum within the tube causes an immediate freezing which is quite different from that encountered in cabinet drying or cabinet pre-treatment of solids in this art. An

entirely different ice crystal structure is developed in this manner which approximates the tiny porous ice crystals formed in the powdered system.

In the filling of the carriers a single pattie or filet is deposited in any suitable manner in the spaces between the plates 39. The carriers 42 are filled right side up because the spacers 38 prevent the patties from falling through. There is always some contact of the pattie product with the transverse plates 39 and so the thermocouple 17 operates accurately in connection with the material undergoing treatment. The filling obviously does not require the use of the curved blades and side rams in this type of operation. After the rate of evaporation is determined for the particular product involved, the thermocouples are set and the drying takes place with the induction system using either the 10,000 or the 60 cycle procedure in exactly the same manner as described earlier in connection with frozen powder products.

At the conclusion of the drying cycle the removal of the carriers is accomplished in precisely the same manner as before. In this instance vibrating equipment is not required because the dehydrated patties or filets are removed by merely inverting the carrier 42 and they drop out freely into the trough and on to the conveyor.

It is important to note that the carriers 34 and 42 are preferably made of aluminum. This is because aluminum is an excellent conductor of heat. However, because of the production of alumina or aluminum oxide and sticking to some degree in certain instances, it is far better to coat each carrier and each plate of each carrier with a thermosetting Teflon which forms a very hard but excellent conducting coating the aluminum so that any interaction or sticking of the product with the aluminum plate becomes impossible. This coating also is necessary in the case of certain fruits which have very high acid contents which would pit and destroy the carriers themselves even after one use. Also, foods with high oils such as fish, where the odor lingers by the porosity of the substance, the hard non-porous surface provided by Teflon is essential.

It is also to be noted at this point that because of the electromagnetic properties of aluminum, it is possible to go down as low as 50 cycles and still produce the necessary degree of heat to accomplish dehydration within a reasonable time. With the 60 cycle phase, the capacitors are not necessary to bring the tubes into resonance for even heating and induction control. Furthermore, in the 50 to 60 cycle phase, each individual coil can have its own generator and this materially lends itself to a more accurate control resulting in better products, as each coil will eventually develop some individual characteristics. It also makes possible the simultaneous processing of different products in individual tubes even in the same tier.

The vapor velocity in the rnanifold 24 should not exceed 60,000 feet per minute. It should preferably be designed for not more than 30,000 feet per minute if the design can be economically so performed. In all cases standard tubing of minimum dimensions is used.

It is to be understood that the carrier as a Whole may be constructed of electrically conducting parts, that is, the spacers and the tie means as well as the plates themselves. Also, for certain types of material such as sticky, oily or those with a strong residual odor, it is desirable to coat all or some of the parts of the carrier with a polyfluorovinyl resin such as Teflon which is a product of the E. I. du Pont Company or other commercial equivalents such as Delrin, also a product by the E. I. du Pont Company.

To aid in the understanding of this method it is to be recalled that by drawing a vacuum the boiling point of the product is lowered. The addition of heat removes the water vapor at the rate of evaporation for the particular product undergoing treatment. Since each type of product has its own rate, this is determined in advance. If the heat goes into the product faster than the rate of evaporation, then there is a melt down, and this is to be avoided. When the water vapor is substantially removed from the product freezing conditions are no lOnger obtained and the temperature of the product slowly rises. It is necessary to set the controls to stop this rise in temperature before any damage is done to the product and still have a completely dry product.

It is also to be understood that induction heating is not the only means of heating the carrier plates, although a very efiicient one. The controlled heating of the plates may be accomplished by directly heating them electrically and with heated fluids.

In general the coil must be designed so that at 100% voltage only a maximum of 2 kw. and a minimum of /a kw. of energy is introduced.

I claim:

1. In the method of vacuum dehydration, the steps of reducing the material to be treated to a frozen snowlike form, packing the snow-like material in a carrier between a plurality of electrically conductive plates, sealing the loaded carrier in a restricted chamber leaving only sufficient room within the chamber for rapid vapor withdrawal, immediately reducing the pressure in the chamber to about 100 microns, heating the chamber by induction current to establish eddy currents with the carrier plates,

instantaneously and continually removing the water vapor from the chamber to reduce the water vapor content of the material to substantially two percent without damaging the material in any way, re-establishing atmospheric pressure in the chamber prior to opening the chamber, emptying the dehydrated material from the carrier and delivering the dehydrated material for packaging or storage.

2. The method of claim 1 wherein the snow-like material is also porous in structure, and the plates of the carrier are aluminum transversely arranged and longitudinally spaced.

3. The method of claim 2 wherein the chamber is a tube constructed of dielectric material wrapped externally with electrically conducting coils insulated from each other and charged with an electric current for interacting with the conductive plates of the carrier producing induction heating within the tube.

4. The method of claim 3 wherein the wrapping coils are tubular and charged with a current having substantially 10,000 cycles.

5. The method of claim 3 wherein the coils are solid and charged with a continuous current having substantially 50 to 60 cycles.

6. The method of claim 3 wherein the operating vacuum is established quickly upon loading of the tube by means of a bleed line in advance of full vacuum line operation.

7. A method of vacuum dehydration, the steps of preparing the material to be treated in preformed portions, placing the preformed portions in a carrier touching and between a plurality of electrically conductive plates of a carrier, sealing the loaded carrier in a chamber leaving only sufiicient open space within the chamber for the rapid removal of the water vapor. Immediately reducing the pressure within the chamber to the order of 100 microns, simultaneously heating the material within the chamber by induction heat sufiicient in time and temperature to reduce the moisture content to less than two percent without damaging the material in any way, instantaneously and continuously removing the water vapor, restoring atmospheric pressure in the chamber with nitrogen gas, removing the carrier from the chamber and emptying the carrier to deliver the finished dehydrated product for packaging or storage.

8. The method of claim 7 wherein the preformed portions are presented in the form of patties of a measured diameter and thickness, and wherein the carrier plates are arranged transversely and spaced longitudinally for the reception of a single pattie, and wherein the open space within the loaded chamber permits the rapid removal of water vapor on all sides of the carrier.

9. The method of claim 8 wherein the chamber is a tube constructed of dielectric material wrapped externally with electrically conducting coils insulated from each other and charged with an electric current for establishing eddy currents with the carrier plates for producing the induction heating within the tube, and maintaining the required temperatures within the tube in timed sequence.

10. The method of claim 9 wherein the coils are tubular and a uniform temperature in the coil wrapping is maintained by circulating a coolant therethrough, and are charged with a current having substantially 10,000 cycles.

11. The method of claim 9 wherein the conductive coil wrapping is solid and charged with a continuous current having substantially 50 to 60 cycles.

12. The method of claim 9 wherein the operating vacuum is established quick-1y upon loading of the tube by means of a bleed line in advance of full vacuum line operation.

13. The method of claim 2 wherein there is a multiplicity of chambers all operating with a single vapor removal and vacuum system, where the heating in each chamber is separately controlled, and where the chambers are operated in groups or tiers, any group of which may be isolated and taken out of operation without afiecting or disrupting the continued operation of the other chambers.

14. The method of claim 7 wherein there is a multiplicity of chambers all operating with a single vapor removal and vacuum system, where the heating in each chamber is separately controlled, and where the chambers are operated in groups or tiers, any group of which may be isolated and taken out of operation without affecting or disrupting the continued operation of the others.

-15. The method of claim 2 wherein there is a multiplicity of chamber all operating with a single vapor removal and vacuum system with the heating in each chamber separately controlled in accordance with product requirements, and wherein each of the chambers is operated separately and may be isolated from the operation of the entire group without affecting or disrupting the continued operation of the other chambers.

16. The method of claim 7 wherein there is a multiplicity of chambers all operating with a single vapor removal and vacuum system with the heating in each chamber separately controlled in accordance with product re quirements, and wherein each of the chambers is operated separately and may be isolated from the operation of the entire group without affecting or disrupting the continued operation of the other chambers.

17. A carrier for vacuum dehydration of food products for use in electrical induction treating tubes comprising in combination a series of transverse electrically conductive plates producing heat by inductive resistance, said plates having a relatively high heat transfer coefficient, arranged vertically in spaced relation, spacers separating the said plates forming a bottom for the carrier, and draw means for holding the plates and spacers in the operative position and form.

18. The carrier of claim 17 in which the plates are circular except at the top where they are cut off in a horizontal chord.

19. The carrier of claim 17 in which the plates are substantially square with all four corners cut to fit the same in a treating tube.

20. The carrier of claim 17 in which all parts are coated with heat conductive polyfluorovinyl resin.

References Cited UNITED STATES PATENTS 5 Rou-t-t 249129 Bierwirth 219-10.75

Albin 21910.75 Craig 34--5 McArthur 219-1075 12 2,875,311 2/ 1959 Harkenrider 21910.49 2,912,553 11/1959 Tudbury 219--10.49 3,238,632 3/ 1966 Voigtlaender-Tetzner 3492 3,364,591 1/1968 Eilen-berg 34-92 WILLIAM J. WYE, Primary Examiner US. Cl. X.R. 

